1. Field of the Invention
The present invention relates to communications systems and, in particular, to an improved system for providing quality-of-service (QoS) in a Voice over IP (VoIP) system.
2. Description of the Related Art
The Internet Protocol (IP) is one of the most popular packet communication and networking protocols being used today. It finds use both on the Internet and in wide area networks (WANs) and local area networks (LANs), such as asynchronous transfer mode (ATM) and Ethernet networks. The promise of inexpensive voice telephony using the Internet has led to extensive interest in “Voice over IP” (VoIP) and “Telephony over LAN” (ToL) applications. In particular, several IP telephony protocols have been developed, including the H.323 Recommendation suite of protocols promulgated by the International Telecommunications Union (ITU), the Session Initiation Protocol (SIP), and Media Gateway Control Protocol (MGCP), to name a few.
For example, FIG. 1A illustrates a protocol stack 100a for a conventional H.323 implementation over an Ethernet IP network. One or more application programs 103a interface to the protocol stack 100a. The H.323 layer 101a includes a control layer 106 supporting H.245 control signaling for negotiation of media channel usage, Q.931 (H.225.0) for call signaling and call setup, and H.225.0 Registration, Admission and Status (RAS). The H.323 layer 101a may also include a data layer 108 supporting T.120 for data conferencing. The H.323 layer 101a further implements audio codecs 102 and may also implement video codecs 104. An RTP/RTCP layer 110 is provided for sequencing the audio and video packets. The H.323 layer 101a employs UDP and TCP 112 as its transport layer, and also employs an IP layer 114, and then, an Ethernet layer 116. Further details concerning the H.323 Recommendation may be obtained from the International Telecommunications Union; the H.323 Recommendation is hereby incorporated by reference in its entirety as if fully set forth herein.
An important key to the development of ToL and VoIP systems is the development of successful Quality of Service (QoS) IP networks. Generally, QoS refers to the ability of a network to guarantee specific performance levels, related to network bandwidth, availability, jitter, security, and data loss. High voice and/or video quality communication require high QoS levels on all network segments involved in the communication. Guaranteed QoS has been of particular concern on Ethernet LANs, both due to the bursty nature of IP traffic and the CSMA/CD contention protocol used by Ethernet.
Several approaches to QoS in IP networks have employed the Type of Service (TOS) byte, i.e., the second byte, in the IP header. The TOS field is an eight-bit field that signals to routers in the network a priority of handling as well as parameters related to delay, throughput, cost, and reliability. Because the TOS field itself had not been widely used, in certain implementations, it has been recast as a “differentiated service” (DS) byte, which is used to indicate to routers the per-hop behavior expected at the node. These approaches, however, do not in themselves provide a Quality of Service. Other protocols, such as the Resource Reservation Protocol (RSVP) or IEEE 802.1 p, are required to implement actual Quality of Service features. Even when the TOS/DS bits are used with such protocols, Quality of Service is not necessarily guaranteed network-wide.
As such, telephony vendors have been developing “Quality of Service Ethernet” (QoSEthernet), which lies between the IP layer and the Ethernet layer in the protocol stack and which provides a guaranteed QoS. Thus, FIG. 1B illustrates a protocol stack 100b including a QoSEthernet layer 115 between the IP layer 114 and the Ethernet layer 116. An exemplary QoSEthernet system is available from Path 1 Network Technologies, Inc., San Diego, Calif., and makes use of RSVP and the intserv process, described by the Internet Engineering Task Force (IETF).
In practice, implementation of the QoSEthernet layer 115 requires modified application programs 103b in order to provide the required QoSEthernet information at call setup. That is, each application program(s) 103b must be modified, or replaced, to provide one or more commands in addition to standard H.323 commands in order to invoke the required QoS. Thus, to support QoSEthernet, a user must not only implement a QoSEthernet layer but also change applications programs, such as telephone, fax, and the like. Further, each application program requires setup and configuration, which can cause added costs and delays in implementation.
As such, there is a need for a system to be able to implement QoSEthernet without having to replace existing software systems. There is a still further need for a system to implement QoSEthernet while using TOS bits to specify the required QoSEthernet Quality of Service.